Tick under valve cover
 

I understand that this is likely a 5th valve issue. V8 5.2 l engone, tick is coming from valve closest to radiator on passenger side. No tick, did oil change 10w-40 new oil then tick started after warmed up and drove.

Q: could this be due to the oil viscosity or lack of? I did use a motor flush and removed filter when changing oil.

I'm prepared to replace the lifer or rod if needed. Any info or links would help, advice as to whether I can run engine with valve cover off to locate which valve rocker assembly is failing.
Thanks.

You sure it's not an exhaust leak at the manifold?

Sticky lifter? Old gunky engine perhaps? Oil viscosity shouldn't be any issue.

I'll second the exhaust leak because sticky lifter is more of a tap.

Im not seeing any smoke from the engine area whatsoever. And I put my head near that valve cover and it's definately coming from that side of the engine. It's a tap for sure. Consistent with the firing at idle.
Sounds like a single rod or lifter because it come and goes with the engines firing order.

You typically won't see smoke from the exhaust leak.

If you feel brave, put on a mechanic's glove and feel around the exhaust manifold for a sharp hot blast of gasses when it fires.

Makes me wonder if a chunk of junk came loose and lodged in a lifter port blocking oil flow to that lifter? May have to do this again.

Checked the exhaust, nothing to report there.
An update however: the tick or ping has ceased except on startup for a mere secound before the oil pressure raises and then it goes away. Now I have experienced the same noise after the oil pressure drops to zero which happens if I exceed 70 mph or long period of driving, all of a sudden the oil pressure will drop and then the sound returns. I'm wondering why the oil pressure is dropping?
Any knowledge or reasoning?

If the engine is all sludged up inside it will take longer for the oil to return to the sump.